A proportional divider is an instrument used by artist and draftsman to maintain scale ratio when transferring design elements from a 3 dimensional object, drawing, or photo to another surface. The two pointed equal length divider legs are attached with an adjustable pivot point that’s selected position is the scaling factor to proportionally make elements larger, smaller or the same size when transferring. The Alvin dividers have scales for equally dividing the length of a line or the circumference of a circle into equal parts, plus with a little math can be used for constructing angles. Here are instructions for using Alvin proportional dividers.